This invention relates generally to magnetic data storage systems, more particularly to magnetoresistive read/write heads, and most particularly to an especially compact write structure.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 includes a sealed enclosure 12, a disk drive motor 14, and a magnetic disk, or media, 16 supported for rotation by a drive spindle S1 of motor 14. Also included are an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (both of which will be described in greater detail with reference to FIG. 2A). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is sometimes termed in the art, to xe2x80x9cflyxe2x80x9d above the magnetic disk 16. With the arm 20 held stationary, data bits can be read along a circumferential xe2x80x9ctrackxe2x80x9d as the magnetic disk 16 rotates. Further, information from concentric tracks can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in an arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A depicts a magnetic read/write head 24 including a read element 26 and a write element 28. Edges of the read element 26 and write element 28 also define an air bearing surface ABS, in a plane 29, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 26 includes a first shield 30, an intermediate layer 32, which functions as a second shield, and a read sensor 34 that is located within a dielectric medium 35 between the first shield 30 and the second shield 32. The most common type of read sensor 34 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element 28 is typically an inductive write element which includes the intermediate layer 32, which functions as a first pole, and a second pole 38. A first pole pedestal 42 may be connected to a first pole tip portion 43 of the first pole 32, and a second pole pedestal 44 may be connected to the second pole tip portion 45 of the second pole 38. The first pole 32 and the second pole 38 are attached to each other by a backgap 40 located distal to their respective pole tip portions, 43 and 45. The first pole 32, the second pole 38, and the backgap 40 collectively form a yoke 41 together with the first pole pedestal 42 and the second pole pedestal 44, if present. The area around the first pole tip portion 43 and the second pole tip portion 45 near the ABS is sometimes referred to as the yoke tip region 46. A write gap 36 is formed between the first pole pedestal 42 and the second pole pedestal 44 in the yoke tip region 46. The write gap 36 is formed of a non-magnetic electrically insulating material. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer 47 that lies between the first pole 32 and the second pole 38, and extends from the yoke tip region 46 to the backgap 40.
Also included in write element 28 is a conductive coil layer 48, formed of multiple winds 49. The conductive coil layer 48 is positioned within a coil insulation layer 50 that lies above the first insulation layer 47. The first insulation layer 47 thereby electrically insulates the coil layer 48 from the first pole 32, while the coil insulation layer 50 electrically insulates the winds 49 from each other and from the second pole 38. In some prior art fabrication methods, the formation of the coil insulation layer includes a thermal curing of an electrically insulating material, such as photoresistive xe2x80x9cphotoresistxe2x80x9d material.
FIG. 2B shows a plan view of the read/write head 24 taken along line 2Bxe2x80x942B of FIG. 2A. This view better illustrates how the coil layer 48 of write element 28 is configured as a spiral with each wind 49 passing around the backgap 40 and beneath the second pole 38 in the region between the backgap 40 and the second pole tip region 45. Because of the magnetic properties of the yoke 41, when a write current is passed through coil layer 48 a magnetic flux is induced in the first and second poles 32 and 38. The write gap 36, being non-magnetic, allows the magnetic flux to fringe out from the yoke 41, thus forming a fringing gap field. Data may be written to the magnetic disk 16 by placing the ABS of read/write head 24 proximate to the magnetic disk 16 such that the fringing gap field crosses the surface of the magnetic disk 16. Moving the surface of the magnetic disk 16 through the fringing gap field causes a reorientation of the magnetic domains on the surface of the magnetic disk 16. As the magnetic disk 16 is moved relative to the write element 28, the write current in coil layer 48 is varied to change the strength of the fringing gap field, thereby encoding data on the surface of the magnetic disk 16 with a corresponding variation of oriented magnetic domains.
Returning to FIG. 2A, a number of parameters that influence the performance of the write element 28 are also shown. The first of these parameters is the yoke length YL, sometimes defined as the distance from the backgap 40 to the first pole pedestal 42. A shorter yoke length YL favors higher data recording rates as it tends to reduce the flux rise time. The flux rise time is a measure of the time lag between the moment a current passed through coil layer 48 reaches its maximum value and the moment the fringing flux field between the first pole 32 and the second pole 38 reaches its maximum. Ideally, the response would be instantaneous, but various factors such as the physical dimensions and the magnetic properties of the yoke 41 cause the flux rise time to increase. A shorter flux rise time is desirable both to increase the rate with which data may be written to a magnetic disk 16, and also to decrease the length of, and the spacing between, data bits on the magnetic disk 16. Shorter data bits more closely spaced together is desirable for increasing the total storage capacity of the magnetic disk 16.
Write elements according to the prior art are manufactured through common photolithography techniques well known in the art involving repeated cycles of masking with xe2x80x9cphotoresist,xe2x80x9d depositing layers of various materials, followed by stripping away remaining photoresist. Each cycle through this process typically fabricates one element of the final structure. Consequently, tolerance for mask misalignment must be accounted for in the designs for these devices. In particular, prior art write elements leave a separation of at least 4 microns between pole pedestals 42 and 44 and the coil layer 48. A similar gap of at least 4 microns is found between the backgap 40 and the coil layer 48. These separations add extra length to the yoke length YL that increases the flux rise time and hinders write performance.
Another parameter of the write element 28 is the stack height SH, sometimes defined as the distance between the top surface of the first pole 32 and the top of the second pole 38, as shown in FIG. 2A. The stack height SH is influenced by the apex angle xcex1, which characterizes the angle of the slope region of the second pole 38 near the yoke tip portion 46 measured relative to a horizontal reference such as the intermediate layer 32. Increasing the stack height SH makes it difficult to control the track width within narrow set tolerances, decreasing the production yield. Consequently, increasing the apex angle xcex1 has the effect of increasing the stack height SH to the detriment of write performance.
A further problem associated with the apex angle xcex1 relates to the magnetic properties of the second pole 38. Increasing the apex angle xcex1 increases the topography over which the second pole 38 must be formed near the yoke tip portion. The second pole 38 is typically formed by sputtering or plating, techniques well suited for producing flat layers, but not as well suited for forming complex surfaces. Consequently, a further problem associated with the apex angle xcex1 is lower production yields resulting from the difficulties encountered in producing uniformity in the second pole 38, especially in the slope region. Still another problem associated with apex angle xcex1 relates to the magnetic properties of the second pole 38 in the slope region, which will be described with reference to FIGS. 3A-3C.
The trend towards higher density recording in the disk drive industry has forced a number of materials changes in the components of the drives, which has, in turn, created additional problems. In particular, in order to achieve higher data densities on the surface of the magnetic disk 16, the traditional magnetic media have not been found to be sufficient. To obtain smaller bits it has been necessary to develop recording media with higher magnetic coercivities. To write to a magnetic medium with a higher magnetic coercivity requires that the write element 28 produce a stronger fringing flux field. To produce a stronger fringing flux field further requires the use of magnetic materials capable of carrying larger magnetic fluxes. In other words, for high density recording applications, new materials for components of the yoke 41 need to have high magnetic saturation (Bs) values.
Permalloy, a nickel alloy containing 20% by weight of iron, is the material most frequently used to form magnetic components of prior art recording devices. However, Permalloy has an unacceptably low Bs for use in high density recording. Consequently, designers of magnetic recording devices have turned to high Bs materials such as nickel alloys containing between 35% and 55% by weight of iron. Replacing Permalloy with higher Bs materials would be a simple matter except for the issue of magnetostriction.
When a material with a non-zero magnetostriction is subjected to a stress, a magnetic field is produced in response. Similarly, when such a material is placed in a magnetic field, a stress in the material develops. Permalloy has been an advantageous material in magnetic recording devices because it has a magnetostriction value of nearly zero. The higher Bs materials, on the other hand, exhibit much higher magnetostriction values. These higher magnetostriction values create additional problems for high density recording applications.
FIGS. 3A-3C illustrate how the apex angle xcex1 coupled with high Bs materials is problematic for high density recording. FIG. 3A shows a plan view of the second pole 38 showing a typical arrangement of magnetic domains 51 as they appear on the top surface of the second pole 38 when fabricated from high Bs materials. Arrows within the magnetic domains 51 indicate the orientations of the domains"" magnetizations. Through much of the body of the second pole 38 the magnetic fields of the domains 51 are favorably oriented perpendicular to the long axis of the second pole 38. However, in the second pole tip region 45 the magnetization of domains 51 are aligned parallel to the long axis of the second pole 38. In the intervening slope region, the magnetic domains are disordered.
FIG. 3B shows a cross-sectional view along the line 3Bxe2x80x943B of FIG. 3A. Similarly, FIG. 3C is an ABS view along the line 3Cxe2x80x943C of FIG. 3B. In FIG. 3C the orientations of the magnetization within the magnetic domains are represented by dots and circled dots. Dots and circled dots show, respectfully, orientations into and out from the plane of the drawing. From FIGS. 3A-3C it can be seen that within the second pole tip region 45 the magnetic domains form a layered structure with magnetization orientations perpendicular to the ABS. This layered structure is sometimes referred to as a striped domain pattern.
It has been found that with increasing apex angle xcex1 the stresses in the magnetic film in the slope region of the second pole 38 also increase. Some of the stress in the magnetic film is inherent from the manufacturing process. Additional stresses may increase during the operation of the read/write head 24 as heat is generated within the device and differences in coefficients of thermal expansion between different materials create minor dimensional changes. The retention of photoresist as an insulator in some prior art devices is especially troublesome in this regard, as photoresist has a relatively large coefficient of thermal expansion. Consequently, photoresist retained beneath the second pole 38 has the effect, when the device is in use, of creating especially large stresses in the slope region of the second pole 38. Therefore, since the effect of magnetostriction is to counteract a stress with a magnetic field, undesirable magnetic fields in the slope region of the second pole 38 tend to increase both as the apex angle xcex1 increases and when photoresist is retained beneath the second pole 38. These undesirable magnetic fields give rise to the striped domain pattern and disordered domains.
The striped domain pattern in the second pole tip region 45 and the disordered domains in the slope region are detrimental to the performance of the write element 28. In particular, these misoriented domains resist changes in the magnetization of the yoke 41. Consequently, when a write current is introduced into the coil layer 48 and a magnetic field is induced in the yoke 41, the flux rise time is lengthened by the resistance to change of the misoriented domains. Longer flux rise times and poorer performance are, therefore, associated with an increasing apex angle xcex1 and with the use of retained photoresist beneath the second pole 38.
FIG. 4 shows a more desirable arrangement of magnetic domains 51 for the second pole 38. Arrows within the magnetic domains 51 indicate magnetic orientation. With such an idealized arrangement, the magnetization of the yoke 41 should respond more quickly to changes in the write current in coil layer 48, thus improving the write performance of the write element 28 by reducing the flux rise time.
Thus, what is desired is a write element with a substantially flat second pole and a shorter yoke length YL. Such a write element would eliminate the apex angle xcex1, have a smaller stack height SH, and would not have the misoriented magnetic domain problems associated with the slope region. Further, it is desired to be able to fabricate a write element without retaining any photoresist as an insulator. It is additionally desired that fabrication of such a write element should be inexpensive, quick, and simple.
The present invention provides a compact structure for a write element of a read/write head of a magnetic data storage device. The structure includes both a substantially flat second pole, significantly less space between the coil and the backgap, and significantly less space between the coil and the pole pedestal. Additionally, a method for the fabrication of such a compact write element is provided.
In an embodiment of the present invention a compact magnetic write structure is provided comprising a conductive shield layer defining a plane, an insulating write gap layer at least partially covering the conductive shield layer, a self-aligned array comprising a conductive pole pedestal and a coil, and a conductive pole layer disposed over the coil and contacting the pole pedestal. The conductive pole layer defines a plane substantially parallel to the plane of the conductive shield layer. The separation between the pole pedestal and the coil is no greater than about 2.0 microns. A further embodiment of the present invention includes both a backgap opening in the insulating write gap layer, and a backgap as part of the self-aligned array. The backgap contacts the conductive shield through the backgap opening.
Additional embodiments of the present invention are directed to a compact MR read/write head that further includes a MR read element. The read element itself comprises two conductive shields separated by an insulator layer in which the MR sensor is disposed, and one of the conductive shields also serves as the first pole of the compact magnetic write structure. Still other embodiments are directed to a magnetic data storage and retrieval system additionally incorporating a magnetic medium and a medium support, where the medium support is capable of supporting the magnetic medium and moving it in relation to the read/write head.
This compact magnetic write structure is advantageous because it provides a substantially flat second pole without a slope region. Eliminating the slope region serves to both reduce the magnetostrictive induced resistance to magnetization changes in the yoke, and to reduce the stack height. Both of these changes reduce the flux rise time and improve writing performance. The structure is further advantageous for limiting the separation between the pole pedestal and the coil to no greater than about 2.0 microns, thereby reducing the yoke length for farther writing performance enhancement. The embodiment in which the separation between the backgap and the coil to no greater than about 2.0 microns is similarly advantageous for further reducing the yoke length. Still another advantage is the ability to fabricate the structure without retaining photoresist as an insulator. This is also advantageous for lowering the flux rise time by reducing unwanted stresses in high Bs magnetic materials caused by large mismatches in coefficients of thermal expansion.
Yet another embodiment of the present invention is directed to a method for manufacturing a magnetic write structure. The method includes providing a substrate including a conductive shield layer and an insulating write gap layer. The conductive shield layer defines a plane, and the insulating write gap layer at least partially covers the conductive shield layer. The method further includes forming over the substrate a self-aligned array comprising a plurality of components including a conductive pole pedestal and a coil. The pole pedestal and the coil contact the write gap layer, and the separation between the pole pedestal and the coil is no greater than about 2.0 microns. Additionally, the method includes forming a conductive pole layer over the self-aligned array. The pole layer is in contact with the pole pedestal and defines a plane that is substantially parallel to the plane of the conductive shield layer. The present invention further includes a planarization step prior to the formation of the pole layer helping to ensure that the plane of the pole layer is substantially parallel to the plane of the conductive shield layer.
Additional embodiments of this invention are directed to a method for manufacturing a magnetic write structure in which the insulating write gap layer is provided with a backgap opening, the plurality of components of the self-aligned array further includes a conductive backgap, and the conductive backgap is disposed above and contacts the conductive shield layer through the backgap opening. The separation between the backgap and the coil in these embodiments is no greater than about 2.0 microns. In still other embodiments a seed layer is formed above and in contact with the insulating write gap layer.
These methods for manufacturing magnetic write structures are advantageous because they incorporate a self-aligned array. A self-aligned array allows the pole pedestal and the coil to be formed with the same mask, thereby allowing these two components to be formed as close together as masking technology will allow without having to leave excess space between them to allow for the possible misalignment of successive masks. Embodiments incorporating a backgap also take advantage of the self-aligned array to minimize the space between the backgap and the coil. A further advantage of the self-aligned array is that it reduces the total number of masking operations needed to form a magnetic write structure, thus saving time and reducing manufacturing costs.
Another advantage of this manufacturing method derives from the planarization step preceding the formation of the pole layer. The planarization achieves three important goals. The first goal is to expose the backgap and the second pole pedestal. The second is to reduce the overall stack height of the finished write structure, improving the write performance of the finished device. The third goal served by the planarization step is that the pole layer formed over the planarized surface is itself substantially flat and substantially parallel to the plane of the conductive shield layer. This serves to simplify the geometry of the pole layer, thereby reducing or substantially eliminating domain striping and further improving write performance of the finished device.